Have a cleared saved game file from the original Tales Of Symphonia on GameCube on your memory card to begin the game with a random set of items.
Successfully complete the game, then load the cleared saved game file to access New Game + mode. You can also now access the Gladsheim dungeon, which will appear on the map during Chapter 8.
Successfully complete the game to unlock the Mania difficulty.
Successfully complete the game on the Mania difficulty to unlock the Unknown difficulty.
Successfully complete the Twilight Palace quests from the Katz Guild to unlock the Twilight Palace dungeon. There will be one of those quests available from Chapter 5 through Chapter 8.
Successfully complete the indicated task to view the corresponding ending sequence:
Bad: Defeat Marta first, then Lloyd during the final battle.
Normal: Lose to Lloyd and Marta during the final battle, then defeat Ratatosk. If you did not make enough good choices during the game, you will get the normal ending.
Good: Lose to Lloyd and Marta during the final battle, then defeat Ratatosk. If you made enough good choices during the game, you will get the good ending.